load flow analysis of phase ii undergrounding alternatives

By KEMA, Inc. Authors: Sedina Eric, Richard Wakefield, Huub Pjustens

KEMA Inc. T&D Consulting, 3801 Lake Boone Trail, Suite 200 Raleigh, NC 27607, Phone: 919 256-0839, Fax: 919 256-0844

December 7, 2004

Load Flow Analysis of Phase II Undergrounding Alternatives

Connecticut Siting Council Load Flow Analysis of Phase II Undergrounding Alternatives December 7, 2004 KEMA Project 04-30

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Legal Notice

This report was prepared by KEMA Inc. as an account of work sponsored by Connecticut Siting Council (CSC). Neither CSC nor KEMA, nor any person acting on behalf of either:

1. Makes any warranty or representation, expressed or implied, with respect to the use of any information contained in this report, or that the use of any information, apparatus, method, or process disclosed in the report may not infringe privately owned rights.

2. Assumes any liabilities with respect to the use of or for damage resulting from the

use of any information, apparatus, method, or process disclosed in this report.

Table of Contents


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Executive Summary............................................................................................................................1 1. Introduction .................................................................................................................................3 2. Analytical Approach.....................................................................................................................4

2.1 Methodology .......................................................................................................................4 2.2 System Data ........................................................................................................................4 2.3 Load data.............................................................................................................................5 2.4 Generation Dispatch.............................................................................................................5 2.5 Power Transfers Between New England and New York..........................................................5

3. Load Flow Studies........................................................................................................................6 3.1 Proposed Alternative using HPFF Cables...............................................................................6 3.2 Alternative with XLPE Technology.......................................................................................7

3.2.1 Proposed Alternative with XLPE Technology ............................................................7 3.2.2 Devon – Beseck Section 20 miles Underground / 20 miles Overhead......................... 10 3.2.3 Devon – Beseck Section 40 miles............................................................................ 13

4. Conclusion ................................................................................................................................. 17 Attachment A Dispatching Scenarios

Attachment B Load Flow Diagram for Applicant’s Proposed Alternative


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Executive Summary The Connecticut Siting Council (“Siting Council”) is conducting a hearing under Docket 272, on the application for a Certificate of Environmental Compatibility and Public Need (“Certificate”) for the construction of new 345 kV and 115 kV electric transmission facilities, located between the Scovill Rock Switching Station in Middletown and the Norwalk Substation in Norwalk, Connecticut. This project is also referred to as “Phase II”. The Connecticut Light and Power and the United Illuminating Company (“Applicant”) submitted the application on October 9, 2003.

In order to fulfill the requirements on burial of the 345 kV lines as directed by the State of Connecticut Public Act No. 04-246, the Siting Council retained KEMA, Inc. to determine the maximum length of the Phase II line that could be installed underground, focusing solely on establishing technical feasibility rather than optimizing the system based on technical performance and economics.

KEMA performed harmonic impedance studies and submitted its report on October 18, 2004. In addition, KEMA conducted load flow studies to investigate whether additional undergrounding beyond the 24 miles proposed in the Application would:

1. worsen thermal and voltage conditions from those indicated in prior Applicant studies of the proposed alternative, or

2. cause voltage and thermal problems that make such undergrounding infeasible.

KEMA performed its load flow analyses by modifying selected load flow cases provided by the Applicant in response to the Towns’ data requests in the discovery process. In making these studies, KEMA substituted XLPE cables for HPFF cables to reduce capacitive charging and improve system harmonic performance.

It is important to note that the original Applicant’s load flow base cases that model the proposed alternative, contain both thermal and voltage criteria violations, under normal and contingency conditions. These violations occur mainly on the local 115 kV lines (six overloads), and on the 115/69 (34.5) kV transformers. The Applicant must address these local criteria violations prior to the final design acceptance. KEMA has assumed that these local violations can be satisfactorily mitigated, but KEMA has made no independent investigation of how this would be accomplished. Instead, KEMA focused on identifying those additional facilities that became overloaded, and the additional voltage violations that occur when XLPE cable was substituted for HPFF cable and when various lengths of the Devon-Beseck corridor were constructed using underground cable.

For the case where the proposed HPFF cable from Norwalk to Devon was replaced with XLPE cable, the load flow studies indicate that the number of overloaded facilities increases in comparison to the number


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of violations identified in the load flow case for the proposed alternative. Most of the overloaded lines are local 115 kV (and below) facilities. Another concern is the overloading of the Plumtree to Triangle line upon the simultaneous loss of two lines (loss of the Plumtree-Middle River line and the Plumtree – Triangle circuit two), and the Plumtree to Middle River line, upon the loss of the double circuit line from Plumtree to Triangle. Mitigation of this overload would likely require either reconductoring the existing lines (if possible) or adding a new circuit.

KEMA’s load flow studies indicate that when an additional 20-mile section of the line extending from Devon toward Beseck was modeled as underground XLPE cable and the rest was modeled as overhead line, the number of contingency overloads increased in comparison to the number of violations identified for the proposed alternative. However, all of the additional overloaded lines continue to be local 115 kV (and below) facilities. Specifically , an additional seven 115 kV facilities became overloaded with such additional undergrounding.

When the full length of the 40-mile corridor from Devon to Beseck was modeled with underground XLPE cable, the number of contingency facility overloads increased further, and two 345 kV circuits overload on contingency. Because of the low impedance of three parallel XLPE cables, the Devon to Beseck underground section reacts as a “sink”, transferring more power to the Southwest Connecticut load pocket, than either the proposed overhead Devon to Beseck line alternative, or the combination 20 miles underground/20 miles overhead alternative. In this case, an overload occurs on each of the two proposed 345 kV underground circuits between Devon and Singer, for a single contingency outage of the identical parallel 345 kV circuit. However, the simultaneous loss of both underground circuits from Devon to Singer, does not result in a thermal overload.

Based on the results of the KEMA’s load flow studies, there is no indication that placing up to 20 miles of the 345 kV line from Devon to Beseck underground would lead to a situation that could not be mitigated either by system reinforcements at voltages of 115 kV (and below) or by adding appropriate voltage support. However, the Applicant would need to address the identified thermal overloads and voltage violations on the local 115 kV(and below) system for its proposed alternative and for the alternatives with extended undergrounding prior to final design. If underground XLPE cable were used for all 40 miles of the Devon-Beseck corridor, a solution would be required for the single contingency 345kV overloads described previously. Such a solution could, in turn, affect system harmonic performance, and further study would be required to determine its acceptability.


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1. Introduction The Connecticut Siting Council (“Siting Council”) is conducting a hearing under Docket 272, on the application for a Certificate of Environmental Compatibility and Public Need (“Certificate”) for the construction of new 345 kV and 115 kV electric transmission facilities, located between the Scovill Rock Switching Station in Middletown and the Norwalk Substation in Norwalk, Connecticut. This project is also referred to as “Phase II”. The Connecticut Light and Power and the United Illuminating Company (“Applicant”) submitted the application on October 9, 2003.

In order to fulfill the requirements on burial of the 345 kV lines as determined by the State of Connecticut Public Act No. 04-246, the Siting Council retained KEMA to investigate what is the maximum length of the Phase II 345 line that could be installed underground, focusing solely on technical feasibility rather than optimizing the system based on technical performance and economics.

KEMA performed harmonic impedance studies and submitted its report on October 18, 2004. In addition, KEMA conducted load flow studies to investigate whether additional undergrounding beyond the 24 miles proposed in the Application would:

1. worsen thermal and voltage conditions from those indicated in prior Applicant studies of the proposed alternative, or

2. cause voltage and thermal problems that make such undergrounding infeasible.

KEMA’s study focused on analysis of the above effects for the conditions that significantly stress the Southwest Connecticut (“SWCT”) transmission system, including:

?? Peak load consistent with the NEPOOL load forecast of 27.7 GW;

??Minimum local generation dispatched;

?? ISO-NE exports to the New York ISO of 700 MW.

KEMA performed its load flow analyses by modifying selected load flow cases provided by the Applicant in response to the Towns’ data requests in the discovery process. In making these studies, KEMA substituted XLPE cables for HPFF cables to reduce capacitive charging and to improve system harmonic performance.


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2. Analytical Approach

2.1 Methodology

KEMA’s load flow studies included the following steps:

1. The HPFF cables proposed for the 24 miles long line section between Norwalk and Devon, were replaced by XLPE cables to reduce capacitive charging;

2. The overhead line section between Devon and Beseck was replaced with a combination of underground and overhead lines, gradually increasing the length of the underground portion from Devon towards Beseck;

3. Steady-state load flow results for each of the XLPE underground options were compared to the steady-state load flow results for the Applicant’s originally proposed alternative.

For steady-state load flow analysis, KEMA used PTI’s PSS/E software (Rev. 29). Normal and contingency analysis were performed using the following criteria:

?? For base case loading performance, transmission lines and transformers were checked against 100% of their normal ratings;

?? For post-contingency loading performance, overloads of transmission lines and transformers were checked against 100% of the long-term emergency ratings;

?? Buses 230 kV and above were checked for voltages less than 95% and greater than 105%. Buses in the 115 kV system were checked for voltages less than 90% and greater than 105%.

Buses and transmission branches on the Connecticut 115 kV system and above were monitored. For the analysis, all tap-changing transformers and phase-shifting transformer adjustments were held fixed. For contingencies involving loss of generation/load the imbalance was made up by the system swing generator located outside New England.

2.2 System Data

KEMA used the load flow base cases provided by the Applicants in response to the Towns’ Data Request No. “Towns-059.” The cases differ based upon: (i) the level and direction of the power transfer between New York and New England, (ii) dispatching scenarios. The base cases are listed in Table 1.


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2.3 Load data

Each load flow base case assumes a total ISO-NE load level of 27.7 GW. The Applicant chose to increase the peak load data from the original peak load estimated for 2006 of 25,718 MW1 to an extreme weather peak of 27,700 MW.2 In actuality, this peak of 27,700 MW approximates IS0-NE’s expected peak load in the year 2012.

2.4 Generation Dispatch

The Applicant used four dispatching scenarios, as shown in Attachment A. Multiple generating units interconnected to the SWCT transmission system were assumed to be out-of-service. The SWCT transmission system is stressed the most when Norwalk Harbor units No. 1 (161MW) and No. 2 (168MW) are not operating, and all the replacing power is transferred from outside resources, as modeled in the Dispatch Scenario 2. In addition, the Dispatch Scenarios 2 and 3 incorporate the assumption that approximately 200 MW is transferred to Northport (LIPA’s substation on Long Island), over the 138 kV submarine cable between Norwalk Harbor and Northport, which simultaneously increases loads on the transmission lines serving SWCT.

2.5 Power Transfers Between New England and New York

With respect to the power transfers between New England and New York the Applicant assumed:

1. Transfers of zero MW;

2. Net transfers from New England to New York of 700 MW;

3. Net transfers from New York to New England of 700 MW.

1 2001 CELT Report and CSC 20-Year Forecast of Loads and Resources. 2 Southwestern Connecticut Reliability Study, January 2002, page 17.

Load Flow Base Case

Transfer between New England and

New York

(MW) 2 3 4 5ph2-alt2 0ph2-alt2-ne-ny 700ph2-alt2-ny-ne -700

Table 1: Load Flow Base Cases

Total Generation in CL&P, UI, CMEEC, & Wallingford Zones for Dispatching

Scenarios 2-5 (MW)

6563 7618 7947 6400


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3. Load Flow Studies Results for the Applicant’s load flow studies indicated that assuming

1) Dispatch Scenario 2 (dispatch with Norwalk Harbor generation units out-of-service while exporting 200 MW to LIPA through the 138 kV submarine cable), and

2) net power transfers of 700 MW from New England to New York (NE-NY)

would create the most stressful3 conditions for the SWCT transmission system.

Consequently, KEMA focused on analyzing the system conditions that resulted from load flow analysis under these assumptions. Those assumptions are incorporated in the Applicant’s original load flow base case titled “ph2-alt2-ne-ny-091503-2.SAV”, provided in response to the Towns’ Data Request No. 05--Q-Towns-059.

3.1 Proposed Alternative using HPFF Cables

The original Applicant’s load flow cases that model the proposed Phase II alternative with the HPFF cables contain both thermal and voltage criteria violations, under both normal conditions and contingency conditions. These violations occur primarily on the local 115 kV lines, and on the 115/69 (34.5) kV transformers. A summary of thermal overloadings under normal and contingency conditions for the load flow base case is provided in Table 2.

Voltage violations under normal and contingency conditions at the 115 kV and above buses are reported in Table 3.

3 See the PowerGEM Report 10021.001-9, July 20, 2004, Page 11

Table 2: Thermal overloadings under normal and contingency conditions in proposed alternative

Bus No.Bus Name kV Bus

No.Bus Name kV Normal Contingency Rating

(MVA)Post-Cont. Flow (MVA)

Overloading%

73172 NORWALK 115 73207 FLAX HIL 115 BASE CASE 256 267 101.473188 BCNFL PF 115 73192 DRBY JB 115 1272-172 1DCT 112 132 129.673207 FLAX HIL 115 73271 RYTN JB 115 1416-1880DCT 256 467 178.673176 TRIANGLE 115 73268 MIDDLRIV 115 1060-1165DCT 134 147 111.373680 WATER ST 115 73681 WEST RIV 115 GRNDAV2TSTK 273 282 100.673162 WATERSDE 115 73168 GLNBROOK 115 SOUTHEND6T 352 367 102.5

From Bus To Bus Conditions


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Bus No. Bus Name kV Initial Voltage

Post Contingency

(p.u.)

Total No of

Violations73160 BALDWINB 115 1.0085 0.8808 273185 BUNKERH 115 1.0179 0.8811 173156 COHNZ JA 115 1.0103 1.0501 273189 FREIGHT 115 1.0195 0.8795 173278 MONT DSL 115 1.0159 1.0553 173177 MYSTICCT 115 1.0176 1.0507 173151 UNCASVLA 115 1.0155 1.0549 273216 WHIP JCT 115 1.0144 1.0516 1

Table 3: Voltage violations under normal and contingency conditions at the 115 kV

The Applicant must address these local criteria violations prior to the final design acceptance. KEMA has assumed that these local violations can be satisfactorily mitigated, but KEMA has made no independent investigation of how this would be accomplished. Instead, KEMA focused on identifying those additional facilities that became overloaded, and the additional voltage violations that occur when XLPE cable was substituted for HPFF cable and when various lengths of the Devon-Beseck corridor were constructed using underground XLPE cable.

A load flow diagram showing power flows over the proposed Phase I and Phase II lines is provided in Attachment B.

3.2 Alternative with XLPE Technology

3.2.1 Proposed Alternative with XLPE Technology

For the case where the HPFF cable from Norwalk to Devon was replaced with XLPE cable, the load flow studies indicate that the number of overloaded facilities increases in comparison to the number of violations identified in the load flow case for the proposed (overhead) alternative. Most of the overloaded lines are local 115 kV (and below) facilities, as summarized in Table 4. Another concern is the overloading of the Plumtree to Triangle line upon the simultaneous loss of two lines (loss of the Plumtree-Middle River line and the Plumtree – Triangle circuit two), and the Plumtree to Middle River line, upon the loss of the double circuit line from Plumtree to Triangle. Mitigation of this overload would likely require either reconductoring the existing lines (if possible) or adding a new circuit.

Replacement of the HPFF cable with the XLPE cable creates two additional voltage violations on the 115 kV buses. (See Table 5.)


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From Bus kV To Bus kV

Conditions: Base Case/

Worst Contingency

Rating (MVA)

Post-Cont. Flow

(MVA)

Overloading% From Bus kV To Bus kV cktConditions:

Base Case/ Worst Contingency

Rating (MVA)

Post-Cont. Flow

(MVA)

Overloading%

NORWALK 115 FLAX HIL 115 BASE CASE 256.0 266.8 101.4 NORWALK 115 FLAX HIL 115 1 BASE CASE 256.0 265.7 101.2BCNFL PF 115 DRBY JB 115 1272-172 1DCT 112.0 132.1 129.6 BCNFL PF 115 DRBY J B 115 1 1272-1721DCT 112.0 132.1 129.7FLAX HIL 115 RYTN JB 115 1416-1880DCT 256.0 467.4 178.6 FLAX HIL 115 RYTN J B 115 1 1880-1977DCT 256.0 440.1 168.3TRIANGLE 115 MIDDLRIV 115 1060-1165DCT 134.0 146.8 111.3 TRIANGLE 115 MIDDLRIV 115 1 1060-1165DCT 134.0 146.8 110.8WATER ST 115 WEST RIV 115 GRNDAV2TSTK 273.0 282.3 100.6 WATER ST 115 WEST RIV 115 1 GRNDAV2TSTK 273.0 282.2 100.6WATERSDE 115 GLNBROOK 115 SOUTHEND6T 352.0 367.3 102.5 WATERSDE 115 GLNBROOK 115 1 SOUTHEND6T 352.0 367.3 102.5

BARBR HL 69 *ROCKVILL 69 1 1625LINE 84.0 93.1 124.8CRRA JCT 115 *ASHCREEK 115 1 1389-1880DCT 439.0 449.1 100.4GLNBROOK 115 *RYTN J B 115 1 1880-1977DCT 289.0 315.5 106.5GRAND AV 115 *WEST RIV 115 1 GRNDAV2TSTK 258.0 272.5 102.6MONTVLLE 115 *DUDLEY T 115 1 1070-1080DCT 183.0 189.2 106.7PLUMTREE 115 *TRIANGLE 115 2 1060-1270DCT 166.0 224.9 134.5PLUMTREE 115 *MIDDLRIV 115 1 1060-1165DCT 126.0 226.0 180.2RYTN J A 115 *NORWALK 115 1 1416-1867DCT 256.0 473.7 181.6SOUTHGTN 345 *SGTN B 115 2 SGTN5TSTK 585.0 585.4 100.1WATERSDE 115 *COS COB 115 1 SOUTHEND6T 239.0 299.1 124.9

Proposed Alternative-HPFF, Dispatch 2, Ne-Ny 700 MW Phase II : Alternative-XLPE Norwalk to Devon, Dispatch 2, Ne-Ny 700 MW Table 4: Comparison of thermal criteria violations between proposed HPFF alternative and XLPE alternative


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Table 5: Comparison of Voltage Violations for Proposed Alternative with XLPE vs. HPFF Cable

Bus No. Bus Name kVInitial

Voltage p.u.

Post Contingency Voltage p.u.

Worst Violation

No. of Violations

Initial Voltage p.u.


Worst Violation

No. of Violations

73160 BALDWINB 115 1.0085 0.8808 2 1.0075 0.8807 273185 BUNKERH 115 1.0179 0.8811 1 1.0169 0.8810 173156 COHNZ JA 115 1.0103 1.0501 2 1.0116 1.0501 273189 FREIGHT 115 1.0195 0.8795 1 1.0184 0.8794 173278 MONT DSL 115 1.0159 1.0553 1 1.0172 1.0553 173177 MYSTICCT 115 1.0176 1.0507 1 1.0188 1.0507 173151 UNCASVLA 115 1.0157 1.0551 2 1.0170 1.0551 173216 WHIP JCT 115 1.0144 1.0516 1 1.0157 1.0516 173210 MONTVLLE 115 1.0172 1.0553 173161 ROCKVILL 115 0.9865 0.7647 1

Proposed Alternative with HPFF Proposed Alternative with XLPE


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Table 6 summarizes power flows over the proposed Phase I and Phase II lines, modeled with XLPE cables, versus HPFF cables.

Table 6: Comparison of Load Flow on System Transmission Corridor Net Power Flow (MW)

From To Base Case HPFF Cables

Base Case XLPE Cable

Beseck 345 kV Devon 345 kV 877 862 Devon 345 kV Singer 345 kV 772 752 Singer 345 kV Norwalk 345 kV 592 570 Plumtree 345 kV Norwalk 345 kV 121 132 Devon 345 kV Devon 115 kV 97.5 102 Singer 345 kV Pequonic & Pequonic

Tap 115 kV 179 180

Norwalk 345 kV Norwalk 115 kV 712 702 Plumtree 345 kV Plumtree 115 kV 446 446

3.2.2 Devon – Beseck Section 20 miles Underground / 20 miles Overhead

KEMA’s load flow studies indicate that when 20 miles of the 345 kV line extending from Devon toward Beseck was modeled as three parallel XLPE cables (of 1750 kcmil) and the remainder was modeled as the proposed overhead line, the number of contingency overloads increases in comparison to the number of violations identified for the proposed alternative. Specifically, an additional seven 115 kV facilities became overloaded with undergrounding of the 20 miles of the line extending from Devon toward Beseck, as summarized in Table 7. All of the overloaded lines are local 115 kV (and below) facilities. The same concern described in Section 3.2.1 is the overloading of the Plumtree to Triangle line upon the simultaneous loss of two lines (loss of the Plumtree-Middle River line and the Plumtree – Triangle circuit two), and the Plumtree to Middle River line, upon the loss of the double circuit line from Plumtree to Triangle. Mitigation of this overload would likely require either reconductoring the existing lines (if possible) or adding a new circuit.

Extension of the XLPE cable creates three additional voltage violations compared to the proposed alternative with HPFF cable, and one compared to the proposed alternative with XLPE cable. This violation is insignificant. (See Table 8.)


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Table 7: Comparison of thermal criteria violations between proposed HPFF alternative and alternative with additional 20 miles undeground XPLE

From Bus kV To Bus kVConditions: Base

Case/ Worst Contingency

Rating (MVA)

Post-Cont. Flow

(MVA)

Overloading %



Rating (MVA)

Post-Cont. Flow

(MVA)

Over. %

NORWALK 115 FLAX HIL 115 BASE CASE 256.0 266.8 101.4 NORWALK 115 FLAX HIL 115 BASE CASE 256.0 267.6 101.5BCNFL PF 115 DRBY JB 115 1272-172 1DCT 112.0 132.1 129.6 BCNFL PF 115 DRBY J B 115 1272-1721DCT 112.0 131.9 129.4FLAX HIL 115 RYTN JB 115 1130LINE 256.0 277.6 105.7 FLAX HIL 115 RYTN J B 115 1130LINE 256.0 467.9 178.5TRIANGLE 115 MIDDLRIV 115 1060-1165DCT 134.0 146.8 111.3 TRIANGLE 115 MIDDLRIV 115 1060-1165DCT 134.0 146.9 111.4WATER ST 115 WEST RIV 115 GRNDAV2TSTK 273.0 282.3 100.6 WATER ST 115 WEST RIV 115 GRNDAV2TSTK 273.0 284.2 101.3WATERSDE 115 GLNBROOK 115 SOUTHEND6T 352.0 367.3 102.5 WATERSDE 115 GLNBROOK 115 SOUTHEND6T 352.0 367.3 102.5

BARBR HL 69 *ROCKVILL 69 1625LINE 84.0 93.1 124.8GLNBROOK 115 *RYTN J B 115 1416-1880DCT 289.0 342.1 115.3MONTVLLE 115 *DUDLEY T 115 1070-1080DCT 183.0 189.3 106.9PLUMTREE 115 *TRIANGLE-ckt 1 115 1165LINE 138.0 145.0 104.9PLUMTREE 115 *MIDDLRIV 115 1060-1165DCT 126.0 226.2 181.2RYTN J A 115 *NORWALK 115 1130LINE 256.0 380.8 145.0WATERSDE 115 *COS COB 115 SOUTHEND6T 239.0 299.1 124.9

Proposed Alternative-HPFF, Dispatch 2, Ne-Ny 700 MW Phase II: 20 miles Underground from Devon to Beseck, XLPE


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Table 8: Effects of Additional 20 miles of Undegrounding with XLPE on Contingency Voltage Violations

Bus No. Bus Name kV Initial Voltage p.u.


Worst Violation

No. of Violations



Worst Violation

No. of Violations

73160 BALDWINB 115 1.0075 0.8807 2 1.0054 0.8803 273185 BUNKERH 115 1.0169 0.8810 1 1.0146 0.8807 173156 COHNZ JA 115 1.0116 1.0501 2 1.0098 1.0501 273189 FREIGHT 115 1.0184 0.8794 1 1.0161 0.8791 173278 MONT DSL 115 1.0172 1.0553 1 1.0155 1.0553 173177 MYSTICCT 115 1.0188 1.0507 1 1.0173 1.0507 173151 UNCASVLA 115 1.0170 1.0551 1 1.0152 1.0551 273216 WHIP JCT 115 1.0157 1.0516 1 1.0140 1.0516 173210 MONTVLLE 115 1.0172 1.0553 1 1.0155 1.0553 173161 ROCKVILL 115 0.9865 0.7647 1 0.9864 0.7646 173476 TRACY05 115 0.9452 0.8996 2

Proposed Alternative with XLPE Alternative with 20 miles UG from D-B


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Table 9 summarizes power flows over the proposed Phase I and Phase II lines, modeled with XLPE cables and 20 miles of additional underground line from Devon toward Beseck, and compares these with power flows for the case with only the undergrounding proposed by the Applicant.

Table 9: Comparison of load flow on system, with additional 20 miles of underground cable

Transmission Corridor Net Power Flow (MW) From To Base Case

XLPE Cable

Base Case XLPE Cables

+ 20 Miles Beseck 345 kV Devon 345 kV 862 975 Devon 345 kV Singer 345 kV 752 854 Singer 345 kV Norwalk 345 kV 570 658 Plumtree 345 kV Norwalk 345 kV 132 64.4 Devon 345 kV Devon 115 kV 102 121 Singer 345 kV Pequonic & Pequonic Tap 115

kV 180 197

Norwalk 345 kV Norwalk 115 kV 702 720 Plumtree 345 kV Plumtree 115 kV 446 452

3.2.3 Devon – Beseck Section 40 miles

When the entire length of the 40-mile corridor from Devon to Beseck is modeled with underground XLPE cable, the number of contingency facility overloads increases further, as summarized in Table 10. Because of the low impedance of three parallel XLPE cables, the Devon to Beseck underground section reacts as a “sink”, transferring more power to the Southwest Connecticut load pocket, than either the proposed overhead Devon to Beseck line alternative, or the combination 20 miles underground/20 miles overhead alternative. In this case, an overload occurs on each of the two 345 kV underground circuits between Devon and Singer, for a single contingency outage of the identical parallel 345 kV circuit. However, the simultaneous loss of both underground circuits from Devon to Singer, does not result in a thermal overload.

Further extension of the XLPE cable generally enhances voltage conditions and eliminates some of the violations associated with the proposed alternative. However, such extension also causes several new 115 kV voltage violations, as summarized in Table 11.


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Table 10: Comparison of thermal criteria violations between proposed HPFF alternative and alternative with additional 40 miles undeground XPLE



Rating (MVA)

Post-Cont. Flow

(MVA)

Overloading %

From Bus kV To Bus kV cktConditions: Base


Rating (MVA)

Post-Cont. Flow

(MVA)

Overloading %

NORWALK 115 FLAX HIL 115 BASE CASE 256.0 266.8 101.4 NORWALK 115 73207 FLAX HIL 115 1 BASE CASE 256.0 272.4 102.9BCNFL PF 115 DRBY JB 115 1272-172 1DCT 112.0 132.1 129.6 BCNFL PF 115 DRBY JB 115 1 1272-172 1DCT 112.0 131.6 128.9FLAX HIL 115 RYTN JB 115 1130LINE 256.0 277.6 105.7 FLAX HIL 115 73271 RYTN JB 115 1 1130LINE 256.0 472.3 179.7TRIANGLE 115 MIDDLRIV 115 1060-1165DCT 134.0 146.8 111.3 TRIANGLE 115 73268 MIDDLRIV 115 1 1060-1165DCT 134.0 146.8 111.2WATER ST 115 WEST RIV 115 GRNDAV2TSTK 273.0 282.3 100.6WATERSDE 115 GLNBROOK 115 SOUTHEND6T 352.0 367.3 102.5 WATERSDE 115 73168 GLNBROOK 115 1 SOUTHEND6T 352.0 367.3 102.5

BARBR HL 69 ROCKVILL 69.9 1 1625LINE 84.0 93.0 124.4BLM JCT 115 NW.HTFD 115 1 1207-1775DCT 228.0 246.2 111.2BLOOMFLD 115 N.BLMFLD 115 1 1207-1775DCT 193.0 216.6 115.4DEVSING2 345 SINGDEV2 345 2 DEVSING1 910.0 1061.6 114.0GLNBROOK 115 73271*RYTN JB 115 1 1416-1880DCT 289.0 342.2 115.2MONTVLLE 115 73611*DUDLEYT 115 1 1070-1080DCT 183.0 189.1 106.5PLUMTREE 115 73176*TRIANGLE 115 1 1165LINE 138.0 145.0 104.7PLUMTREE 115 73268*MIDDLRIV 115 1 1060-1165DCT 126.0 226.1 180.9RYTN J A 115 73172*NORWALK 115 1 1130LINE 256.0 474.1 179.6SINGER 345 73313 SINGDEV2 345 1 DEVSING1 910.0 1050.5 112.8WATERSDE 115 73163*COS COB 115 1 SOUTHEND6T 239.0 299.1 124.9

Proposed Alternative-HPFF, Dispatch 2, Ne-Ny 700 MW Phase II :40 miles Underground from Devon to Beseck, XLPE


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Table 11: Effects of Additional 20 miles and 40 miles of Undegrounding on Contingency Voltage Violations

Bus No. Bus Name kVInitial Voltage

p.u.


Worst Violation

No. of Violations



Worst Violation

No. of Violations



Worst Violation

No. of Violations

73160 BALDWINB 115 1.0075 0.8807 2 1.0054 0.8803 2 1.0078 0.8820 273185 BUNKERH 115 1.0169 0.8810 1 1.0146 0.8807 1 1.0170 0.8823 1

73156 COHNZ JA 115 1.0116 1.0501 2 1.0098 1.0501 2

73189 FREIGHT 115 1.0184 0.8794 1 1.0161 0.8791 1 1.0186 0.8808 173278 MONT DSL 115 1.0172 1.0553 1 1.0155 1.0553 1

73177 MYSTICCT 115 1.0188 1.0507 1 1.0173 1.0507 173151 UNCASVLA 115 1.0170 1.0551 1 1.0152 1.0551 2

73216 WHIP JCT 115 1.0157 1.0516 1 1.0140 1.0516 173210 MONTVLLE 115 1.0172 1.0553 1 1.0155 1.0553 1

73161 ROCKVILL 115 0.9865 0.7647 1 0.9864 0.7646 1 0.9873 0.7671 173476 TRACY05 115 0.9452 0.8996 2

73682 ELMWST A 115 1.0305 0.8810 373683 ELMWST B 115 1.0305 0.8774 3

73671 NO.HAVEN 115 1.0337 1.0518 1

Proposed Alternative with XLPE Alternative with 20 miles UG from D-B Alternative with 40 miles UG from D-B


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Table 12 summarizes power flows over the proposed Phase I and Phase II lines, modeled with XLPE cables and 40 miles of additional underground line from Devon toward Beseck, and compares these with power flows for the prior two cases.

Table 12: Comparison of load flow on system, with additional 20 and additional 40 miles of underground cable

Transmission Corridor Net Power Flow (MW) From To Base Case XLPE

Cable Base Case

XLPE Cables + 20 Miles

Base Case XLPE Cables

+ 40 Miles Beseck 345 kV Devon 345 kV 862 975 1263 Devon 345 kV Singer 345 kV 752 854 1094 Singer 345 kV Norwalk 345 kV 570 658 854 Plumtree 345 kV Norwalk 345 kV 132 64.4 -104 Devon 345 kV Devon 115 kV 102 121 169 Singer 345 kV Pequonic & Pequonic

Tap 115 kV 180 197 237

Norwalk 345 kV Norwalk 115 kV 702 720 750 Plumtree 345 kV Plumtree 115 kV 446 452 468

Note: A negative value indicates a power flow in the opposite direction.


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4. Conclusion The original Applicant’s load flow base cases that model the proposed alternative, contain both thermal and voltage criteria violations, under normal and contingency conditions. These violations occur mainly on the local 115 kV lines (six overloads), and on the 115/69 (34.5) kV transformers. The Applicant must address these local criteria violations prior to the final design acceptance. KEMA has assumed that these local violations can be satisfactorily mitigated, but KEMA has made no independent investigation of how this would be accomplished. Instead, KEMA focused on identifying those additional facilities that became overloaded, and the additional voltage violations that occur when XLPE cable was substituted for HPFF cable and when various lengths of the Devon-Beseck corridor were constructed using underground cable.

For the case where the proposed HPFF cable from Norwalk to Devon was replaced with XLPE cable, the load flow studies indicate that the number of overloaded facilities increases in comparison to the number of violations identified in the load flow case for the proposed alternative. Most of the overloaded lines are local 115 kV (and below) facilities. Another concern is the overloading of the Plumtree to Triangle line upon the simultaneous loss of two lines (loss of the Plumtree-Middle River line and the Plumtree – Triangle circuit two), and the Plumtree to Middle River line, upon the loss of the double circuit line from Plumtree to Triangle. Mitigation of this overload would likely require either reconductoring the existing lines (if possible) or adding a new circuit.

KEMA’s load flow studies indicate that when an additional 20-mile section of the line extending from Devon toward Beseck was modeled as underground XLPE cable and the rest was modeled as overhead line, the number of contingency overloads increased in comparison to the number of violations identified for the proposed alternative. However, all of the additional overloaded lines continue to be local 115 kV (and below) facilities. Specifically, an additional seven 115 kV facilities became overloaded with such additional undergrounding.

When the full length of the 40-mile corridor from Devon to Beseck was modeled with underground XLPE cable, the number of contingency facility overloads increased further, and two 345 kV circuits overload on contingency. Because of the low impedance of three parallel XLPE cables, the Devon to Beseck underground section reacts as a “sink”, transferring more power to the Southwest Connecticut load pocket, than either the proposed overhead Devon to Beseck line alternative, or the combination 20 miles underground/20 miles overhead alternative. In this case, an overload occurs on each of the two proposed 345 kV underground circuits between Devon and Singer, for a single contingency outage of the identical parallel 345 kV circuit. However, the simultaneous loss of both underground circuits from Devon to Singer, does not result in a thermal overload.


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Based on the results of the KEMA’s load flow studies, there is no indication that placing up to 20 miles of the 345 kV line from Devon to Beseck underground would lead to a situation that could not be mitigated either by system reinforcements at voltages of 115 kV (and below) or by adding appropriate voltage support. However, the Applicant would need to address the identified thermal overloads and voltage violations on the local 115 kV (and below) system for its proposed alternative and for the alternatives with extended undergrounding prior to final design. If underground XLPE cable were used for all 40 miles of the Devon-Beseck corridor, a solution would be required for the single contingency 345kV overloads described previously. Such a solution could, in turn, affect system harmonic performance, and further study would be required to determine its acceptability.


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Attachments


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Attachment A

Dispatching Scenarios


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Table A-1: Dispatching Scenarios

Dispatch (MW) Bus Name 4 KV BUS# 2 3 4 5

AESTH PF 20 73538 180 180 180 180BATES DA 0.48 73351 0 0 0 0BCNFL PF 115 73188 0.9 0.9 0.9 0.9BCNFL PF 115 73188 1.5 1.5 1.5 1.5BCNFL PF 115 73188 1 1 1 1BE 10 ST 16 73654 0 180 180 0BE 11 16 73652 0 170 170 0BE 12 16 73653 0 170 170 0BPTHBR#2 20 73647 0 0 0 0BPTHBR#3 22 73648 375 375 375 375BPTHBR#4 13.8 73649 0 0 0 0BULLS BR 27.6 73381 5 5 5 5CAMPV PH 115 73203 3 3 3 3CAMPV PH 115 73203 3 3 3 3CAP D PF 13.8 73545 28.2 28.2 28.2 28.2CAP D PF 13.8 73545 21.8 21.8 21.8 21.8COS COB 115 73163 0 0 0 0COS COB 115 73163 0 0 0 0COS COB 115 73163 0 0 0 0CRRA PF 11.5 73547 32 32 32 32CRRA PF 11.5 73548 32 32 32 32CRRRA PF 13.8 73650 57 57 57 57DEVGAS11 13.8 73570 0 0 0 0DEVGAS12 13.8 73571 0 0 0 0DEVGAS13 13.8 73572 0 0 0 0DEVGAS14 13.8 73573 0 0 0 0DEVON 345 73297 0 0 0 0DEVON#7 13.8 73553 106 106 106 0DEVON#8 13.8 73554 106 106 106 0DEVON10 115 73277 0 0 0 0DEXTR PF 13.8 73539 26.2 26.2 26.2 26.2DEXTR PF 13.8 73539 11.8 11.8 11.8 11.8ENGLISH7 13.8 73657 0 0 0 0ENGLISH8 13.8 73658 0 0 0 0EXETR PF 115 73281 26 26 26 26FORST PF 13.8 73536 13 13 13 13FRKLN DR 13.2 73543 0 0 0 0GLNBROOK 115 73168 0 0 0 0LAKERD#1 21 73565 280 280 280 280LAKERD#2 21 73566 280 280 280 280LAKERD#3 21 73567 280 280 280 280LISBN PF 115 73276 13.5 13.5 13.5 13.5

4 These are the bus names assigned by the Applicant in their power flow cases, which was provided in the Townships’ data request number ##. For a definition of the acronyms in use, please see the response to the original data request.


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Table A-1: Dispatching Scenarios (Continued)

Dispatch (MW) Bus Name KV BUS# 2 3 4 5

MERIDEN1 21 73588 195 195 195 195MERIDEN2 21 73589 195 195 195 195MERIDEN3 21 73590 196 196 196 196MIDD#10J 13.2 73564 17 17 17 17MIDDTN#2 13.8 73555 117 117 117 117MIDDTN#3 22 73556 233 233 233 233MIDDTN#4 22 73557 400 400 400 400MILFD#1 13.8 73574 280 280 280 0MILFD#2 13.8 73575 0 280 280 0MILL#2 24 73562 860 860 860 860MILL#3 24 73563 1140 1140 1140 1140MONT DSL 115 73278 0 0 0 0MONT DSL 115 73278 0 0 0 0MONTV#5 13.8 73558 81 81 81 81MONTV#6 22 73559 402 402 402 402NH HARBR 22 73651 447 447 447 447NORHAR#1 18 73551 0 0 161 161NORHAR#2 20 73552 0 0 168 168NORWALK 345 73293 0 0 0 0RKRIV PF 115 73280 2.6 2.6 2.6 2.6ROCK RIV 13.8 73541 25 25 25 25RVRSD PF 23 73537 0 0 0 0SANDH DB 0.48 73352 0 0 0 0SANDH DC 0.48 73353 0 0 0 0SCRRA PF 69 73616 13.2 13.2 13.2 13.2SHEPAUG 69 73341 32 32 32 32SMD1112J 13.8 73549 0 0 0 0SMD1112J 13.8 73549 0 0 0 0SMD1314J 13.8 73550 0 0 0 0SMD1314J 13.8 73550 0 0 0 0SMEAD PF 23 73546 3 3 3 3SMEAD PF 23 73546 10 10 10 10STEVENSN 115 73187 0 0 0 0TUNNEL 23 73544 0 0 0 0TUNNEL 69 73617 17 17 17 17WALL LV1 13.8 73594 0 51 51 0WALL LV1 13.8 73594 0 51 51 0WALL LV2 13.8 73595 0 51 51 0WALL LV2 13.8 73595 0 51 51 0WALL LV3 13.8 73596 0 51 51 0WLNGF PF 115 73631 6.4 6.4 6.4 6.4WNDSRLK 27.6 73459 8 8 8 8


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Attachment B

Load Flow Diagram for Applicant’s Proposed Alternative Peak Load, No Contingencies


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load flow analysis of phase ii undergrounding alternatives

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